Field of the Invention
The present invention relates to a circuit configuration for a charge pump and also to a voltage regulator in which a circuit configuration of this type is used in a charge pump.
The operation of various electronic circuits necessitates the use of voltage regulators that ensure that the operating voltage is as far as possible free from interference and stabilized. Thus, by way of example, electronic units in motor vehicles require voltage regulators which produce an interference-free, stabilized output voltage (of the order of magnitude of approximately 5 V) from the operation voltage (between 12 and 15 V) on which interference is superposed. The voltage regulators used in this field of application must have a very low current consumption (&lt;100 .mu.A) since the majority of electronic motor vehicle systems remain connected to the on-board electrical system of the motor vehicle even when the motor vehicle is turned off, but the vehicle battery must not be discharged in his case. Furthermore, the voltage regulators used should enable the smallest possible voltage drop between the input and output voltages, in order that an output voltage which is still sufficiently high can be maintained even in the event of dips in the supply voltage or on-board electrical system voltage to 5.5 V, for example.
Charge pumps are frequently used for driving power MOS transistors. To ensure that the charge pump circuit used in this context manages with the smallest possible integrated capacitors, it must, however, be operated at the highest possible frequency, as a result of which, however, the problem of electromagnetic radiation arises. In order to counteract this problem, Published, European Patent Application EP 0 633 662 A1, for example, has proposed a charge pump including a circuit configuration which generates a variety of signals which are nested in one another, in each case two of these signals having flattened edges having precisely complementary profiles with respect to one another, which edges lead to a lower degree of electromagnetic radiation of the charge pump. The circuit configuration described in Published, European Patent Application EP 0 633 662 A1 essentially corresponds to a ring oscillator with two series circuits formed by a plurality of driver stages, the output of the last driver stage of one series circuit being connected to the input of the first driver stage of the other series circuit. The outputs of the driver stages of the individual series circuits are connected to one another via holding stages formed, by way of example, by in each case two inverters connected up oppositely to one another. Inverted output signals can be picked off at the outputs of the individual driver stages. As has already been explained, this circuit configuration can be used to suppress emitted interference, which is of considerable importance in the case of voltage regulators. However, the charge pump described in Published, European Patent Application EP 0 633 662 A1 generates square-wave output signals, as a result of which interference continues to be emitted in principle, albeit in a weakened form.